Generic pistons of this type, when used as brake pistons in disc brakes, are among others also responsible for the production and/or transmission of undesirable brake noises. To reduce such brake noises, the brake pistons normally have an appropriate configuration. German patent application No. 38 33 552, for example, discloses a spot-type disc brake which has a generic bowl-shaped brake piston. The bowl-shaped brake piston bears with one front side against the back side of a brake lining, and the bowl bottom faces the hydraulic pressure chamber in the brake housing. On its end surface facing the friction lining, the brake piston has a step, with the result of a sickle-shaped, rather than an annular, abutment surface between the brake piston and the friction lining back plate. Such a sickle-shaped abutment between the brake piston and the brake lining produces a slight shift in the resulting pressure point between the brake piston and the brake lining and results in a positive reduction of brake noises. The result of such a modification of the brake piston for noise reduction purposes is the requirement of a true-to-size orientation or positioning of the brake piston within the brake cylinder, in particular in order to avoid an undesirable inclined positioning of the piston-side brake lining. Such a positioning is especially related to the exact angular position of the piston in relation to a rotation about the cylinder bore axis. In prior art brake piston designs, it is only to an insufficient extent not possible to position the brake piston inside the brake cylinder with sufficient accuracy to achieve the noise reduction results attained by the present invention.
An object of the present invention is to provide a piston for a hydraulic piston-and-cylinder assembly which is easy to mount and can be placed in a defined position within a cylinder bore.
Preferably, the piston includes a key-type tool accommodation suited for engagement by a mounting means of a corresponding configuration and intended for the defined positioning of the piston inside a cylinder bore. Thus, the piston can be arranged in a true-to-size fashion within a cylinder bore during the installation of the piston in the cylinder bore. More particularly, this ensures precisely maintaining the angular position with respect to a rotation about the cylinder bore axis.
According to a favorable design variation, the mounting means, which is particularly configured as a mating mounting tool, and the correspondingly configured accommodation in the piston are form-lockingly engaged similar to a male-female plug assembly. This permits applying the mounting means or tool only in one single position on the accommodation in the piston, thereby allowing a defined alignment of the piston inside the cylinder bore.
It is especially favorable to configure the above-mentioned accommodation on one of the front surfaces of the cylindrical piston or, with a substantially bowl-shaped configuration of the piston (as is the case particularly with brake pistons), on the inner surface of the brake piston bowl.
A design variation of the key-type accommodation which is particularly easy to achieve, results from the provision of a corresponding recess or projection on the piston. A recess or projection of this type permits, as has already been mentioned, the key-type defined engagement or application of an associated mounting means and has a correspondingly shaped contour (as can be taken from the drawings in particular).
Preferably, at least one of the end surfaces of the cylindrical piston has an inclined positioning, at least in sections, with respect to a plane which extends vertically to the direction of piston displacement. This achieves for a brake piston in a normal brake operation an inclined positioning of the piston inside the cylinder bore which is favorable to prevent brake noises. Favorably, a step which extends in a secant's direction of the piston takes its course through the chamfered surface. In its depth in the direction of piston displacement, this step is so dimensioned that it can be used for the exact positioning of the piston during installation by making use of optical means (for example, Laser, monitoring by means of pictures, video, etc.) for detection of the position of the piston. In a combination with the described positioning device for the brake piston, this permits taking effect on the development of brake noises.